Connecting rods which connect piston pins and crankpins have been widely employed in engines for vehicles, for example. A connecting rod has a larger end connected to the crankpin and a smaller end connected to the piston pin. For manufacturing a connecting rod, it is customary to integrally form a connecting rod from the larger end to the smaller end by forging or the like, for example, and then crack the larger end into a cap part and a rod part.
A method of cracking a connecting rod disclosed in Japanese Laid-Open Patent Publication No. 10-277848, for example, comprises the steps of providing an internal pressure applying device for applying an outward internal pressure to a bearing hole in the bearing of a connecting rod and a pair of external pressure applying devices for applying an external pressure to the bearing, applying an external pressure to the bearing from the pair of external pressure applying devices and an internal pressure to the bearing from the internal pressure applying device, and instantaneously releasing the external pressure from the external pressure applying devices while the internal pressure to the bearing from the internal pressure applying device is of a level capable of cracking the bearing, thereby enabling the internal pressure to instantaneously crack the bearing.
Japanese Laid-Open Patent Publication No. 2002-66998 discloses an apparatus for fracturing a connecting rod, comprising first and second support members for horizontally supporting a connecting rod, the first and second support members being disposed on a base of a pallet for placing the connecting rod thereon and movable in directions away from each other, a split mandrel having mandrel halves vertically mounted on the first and second support members and having respective outer circumferential surfaces for abutment against respective inner surfaces of an opening part, a wedge having tapered surfaces abutting against confronting end surfaces of the mandrel halves, for uniformly separating and spreading the mandrel halves away from each other, an actuator for applying a load to the wedge, and a control circuit for applying an initial load to the actuator to bring the mandrel halves into abutment against the respective inner surfaces of the opening part and thereafter applying a fracture load to the opening part for instantaneously fracturing.